Steam generator

ABSTRACT

A steam generator has a boiling chamber receiving water from a reservoir through a capillary tube and discharging steam through an outlet having a selectively variable orifice size. A pair of spaced electrodes in the form of metal strips are suspended within the chamber and are connected across a voltage source. The lower portion of each metal strip has conductive portion of larger area than the upper portion thereof. The enlarged area extends from the vicinity of the chamber bottom to about the middle third of the chamber. The electrodes can be formed by a pair of flat metal strips disposed in parallel vertical planes and each having an enlarged portion of either constant or variable width. Alternatively, each electrode can be formed from a strip bent in its dimension of thickness to form a &#39;&#39;&#39;&#39;J&#39;&#39;&#39;&#39; configuration. The pair of J-shaped electrodes are vertically supported in nested relationship in either identical or inverted orientation.

United States Patent [72] Inventor Nat Camp Homestead Place, Harrison,N.Y. 10528 [21] Appl. No. 11,986 [22] Filed Feb. 17, 1970 [45] PatentedNov. 9, 1971 Continuation-impart of application Ser. No. 826,870, May22, 1969, now abandoned.

[54] STEAM GENERATOR 5 Claims, 7 Drawing Figs.

[52] US. Cl. 219/288, 219/273, 219/293, 239/136 [51 Int. Cl 1105b 3/60[50] Field 01 Search ..219/284-295,

. 271-276;2l/ll8, 119; 239/133, 135,

[56] References Cited UNITED STATES PATENTS 2,806,932 9/1957 Conlin eta1. 219/275 2,885,527 5/1959 Tone et al 219/289 X 2,818,486 12/1957Schmitt et al.. 218/288 X 1,782,069 11/1930 Henning 219/289 3,219,79611/1965 Grafet a1 219/273 X 3,267,678 8/1966 Camp 219/272 UX FOREIGNPATENTS 241,130 10/1962 Australia 219/288 108,664 10/1943 Sweden 219/285Primary Examiner-A. Bartis Attorney-Karl F. Ross ABSTRACT: A steamgenerator has a boiling chamber receiving water from a reservoir througha capillary tube and discharging steam through an outlet having aselectively variable orifice size. A pair of spaced electrodes in theform of metal strips are suspended within the chamber and are connectedacross a voltage source. The lower portion of each metal strip hasconductive portion of larger area than the upper portion thereof. Theenlarged area extends from the vicinity of the chamber bottom to aboutthe middle third of the chamber. The electrodes can be formed by a pairof flat metal strips disposed in parallel vertical planes and eachhaving an enlarged portion of either constant or variable width.Alternatively, each electrode can be formed from a strip bent in itsdimension of thickness to form a 1" configuration. The

pair of J-shaped electrodes are vertically supported in nestedrelationship in either identical or inverted orientation.

STEAM GENERATOR CROSS-REFERENCE TO RELATED APPLICATION This applicationis a continuation-impart of my application Ser. No. 826,870, filed May22, 1969 now abandoned.

BACKGROUND OF THE INVENTION This invention relates generally to a steamgenerator of the type described in my prior U.S. Pat. No.3,267,678,1aued Aug. 23, I966, which discloses a vapor-generating devicewherein water from a relatively large body of liquid in a storage tank,or the like, is electrically heated in a relatively small-boilingchamber, the evaporating liquid being continuously replenished by way ofa capillary tube connecting an inlet of the boiling chamber to thesupply tank.

Such a system works well when the outlet from the steam chamberterminates in a fixed nozzle orifice generating a substantially constantback pressure, which, together with the substantially constant inletpressure delivered by the capillary tube, maintains the water within theboiling chamber at a more or less constant level at which the liquidinflux due to the pressure differential just balances the rate ofevaporation. If, however, the effective orifice opening is changed tovary the width of the emitted jet,the liquid level in the boilingchamber may change so much as to lead to a flooding or a draining of thechamber unless a compensatory adjustment is made in the wattageconsumed.

SUMMARY OF THE INVENTION Generally speaking, it is an objectof theinvention to provide improved water-heating means in a boiling chamberwhich will stabilize wattage and substantially reduce the possibility offlooding or draining of the boiling chamber.

More specifically, my invention aims at providing means for maintaininga substantially constant water level in a boiling chamber of a steamgenerator to which water is fed at a controlled rate by way of arestricted supply conduit, such as the aforementioned capillary tube,and to maintain a low water level while enabling control of the vaporstream over a wide range of widths by merely varying the nozzle sizewithout any other adjustment.

It is known that water can be heated by the immersion to twospaced-apart electrodes connected across a voltage source, the rate ofheat generation being proportional to the current flow, which increasesprogressively with the depth of immersion and the resulting decrease inthe effective electrical resistance of the water bath if the width ofthe electrodes is substantially constant throughout their height. If theelectrodes terminate at the bottom of the chamber in such a manner as tohave greater facing areas, the current flow along their stems becomesnegligible and the rate of heating is almost independent of the depth ofimmersion.

Although electrodes of the first-mentioned type could be used toregulate the water level in the presence of a constant supply voltage,they tend to draw excessive current if the boiling chamber is filled toan extent considerably above the normal level before the current isturned on.

It is, accordingly, a more specific object of my present invention toprovide level-regulating electrodes for the purpose set forth whichminimize spitting resulting from too rapid boiling and which do notoverload the power supply though allowing for a considerable variationin the current rate, depending on the water level in the boilingchamber, to generate the requisite amount of heat for overcomingdifferent back pressures created in the boiler through a restrictableoutlet.

The aforesaid objects are realized, pursuant to my present invention, bythe provision of a pair of generally upright parallel electrodesreaching from above into a water bath within a boiling chamber whichreceives its water supply through a restricted inlet, such as acapillary tube, and which is provided with an adjustable outlet, the twoelectrodes including a pair of parallel conductive elements rising to anintermediate level of the chamber. These conductive elementsareconstructed and arranged to form facing portions of greater area, as byhaving enlarged or internested lower portions. More specifically, theenlarged areas should extend from the vicinity of the chamber bottom toabout the middle third of the chamber to provide an adequate range oflevel variations therealong while ensuring the existence of a sufficientvapor space above the water level to prevent boiling out or spitting" ofhot water.

With a pair of such electrodes, control of the water level within thelower part of the chamber is possible since any rise of that level alongthe immersed conductive elements results in a rapid increase in theeffective electrode area with a consequent rise in heating current andgreater vaporization rate; if, upon a lowering of the back pressure dueto anenlargement of the effective chamber outlet, liquid enters thechamber more rapidly through the capillary inlet tube, the rise in waterlevel sharply increases the magnitude of the heating current so as torestore the balance.

Once the liquid has reached the upper boundary of the main electrodeportions, a further rise in water level entrains only a relativelyslight increase in heating current, or none at all if the exposedelectrode surface does not rise above the middle region of the chamber,so that the power supply will not be overloaded even if the chamber iscompletely filled when the circuit is closed. In that event, the levelgradually drops back, at a rate depending upon the width of the nozzleorifice, .until the aforedescribed balance is attained.

BRIEF DESCRIPTION OF THE DRAWING For a fuller understanding of theinvention, reference is had to the following description taken inconnection with the accompanying drawing, in which:

FIG. 1 is adiagrammatic sectional view of a steam generator generallysimilar to that described in my aforementioned U.S. Pat. No. 3,267,678,but provided with a boiling chamber containing a pair of electrodesconstructed in accordance with an embodiment of the present invention;

FIG. 2 shows at (A) a diagrammatic face view of an embodiment of theelectrodes of FIG. I and at (B) a graph serving to explain the operationof the system;

FIGS. 3-5 are views similar to FIG. 2(A), illustrating differentelectrode shapes capable of being used in the system of FIG. 1;

FIG. 6 is an enlarged sectional view of a boiling chamber incorporatinganother embodiment of electrodes constructed in accordance with theinstant invention; and

FIG. 7 is a sectional view taken along the line 77 of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, I have illustrated asteam generator comprising a liquid reservoir in the form of a tank I0having a drain II connected via a capillary tube 12 to an inlet 13 of anupright boiling chamber 14. A strainer 15 overlies the drain II to keepimpurities away from the tube 12. Chamber I4 has a top 16 in the form ofa detachable lid from which an outlet tube 17 leads to a head 18carrying a turret 19 with a set of nozzles 20 of different orificesizes. Turret 19 may be rotated to align any one of the nozzles 20 withthe outlet tube 17 in order to throttle the discharge of steam therefromto a predetermined extent.

A pair of electrodes 21, 22 are suspended from lid 16, hanging down toalmost the bottom of chamber 14 in spaced-apart, parallel relationship.These electrodes are connectable by way of a switch 23 across a sourceof operating voltage diagrammatically indicated at 24.

The water level in tank 10, whose volume greatly exceeds that of boilingchamber 14, is above the top of the chamber so as to create a sufficienthydrostatic pressure differential across capillary tube 12 to drivewater into the chamber. With the twin electrodes 21, 22 energized, thesteam generated in chamber I4 creates a back pressure whose' magnitudedepends upon the effective width of the selected nozzle 20. The amountof heating current passing between the electrodes 2] and 22 depends onthe quantity of water bridging these electrodes and is therefore afunction of the height h of the liquid in chamber 14. Thus, the waterlevel in the chamber during steady state operation must be such thatenough heat is generated to raise the temperature of the water bathabove the boiling point (which varies somewhat with the back pressure ofthe steam), taking into account the constant influx of cold water fromreservoir to balance the rate of vapor discharge via the selected nozzle20.

In FIG. 2(A) I have shown an advantageous shape of the electrode 21,which, of course, is also representative of the similar companionelectrode 22. This electrode consists of a metal strip (e.g. of steel)of substantial constant width w bent roughly into the shape of a J, withthe hook 21a of the J terminating at a level L which may be in themiddle third of its length. Other levels indicated in FIG. 2 are thechamber bottom L the lower end of the electrode at L,, the upper edge ofthe transverse bar 21b of the J at L and the top of the electrode at LThe operation of the system of FIG. 1, whose electrodes 21, 22 have theshape illustrated in FIG. 2(A), will now be explained with reference tothe graph of FIG. 2(B). In this graph, I have plotted the water volume vand the heating current I (on the abscissa) against the height of thewater level (on the ordinate), it being understood that this showing isto be considered qualitative rather than quantitative.

With chamber 14 of cylindrical or prismatic configuration, volume vvaries proportionately with height h as indicated by the straightdot-dash line in FIG. 2.

The heating current I, and therefore the amount of thermal energygenerated, varies the conductance of the water body between theelectrodes and is thus generally proportional to the immersed electrodearea. This is represented by the solid line in FIG. 2 according to whichthe slope dI/dh is proportional to the width w of the electrode strip inthe region L:,L has twice this magnitude in the region L L in which theeffective width is doubled, and is still greater in the bottom regionL,L

Significant for the proper operation of the system of FIG. 1 is the factthat the heating current rises more rapidly than the water volumebetween levels L, and L thereafter increasing more slowly than thatvolume.

Upon prolonged standing with switch 23 open, water from reservoir 10completely fills the chamber 14. When the switch is then closed,electrodes 21 and 22 draw a starting current I having the magnitudeshown in FIG. 2(B). This current is only slightly greater than thecurrent 1;, flowing when the liquid is at the intermediate level L;,.

After the necessary warmup period, which will be quite short if thevolume of chamber 14 is small, steam begins to evolve and to exit fromthe chamber via one of the nozzles 20. when the rate of steam generationoutraces the water supply through tube 12, the water flow through tube12 reverses so that the liquid volume decreases at a faster rate thanthe current flow as will be apparent from the diagram from FIG. 2(B).

This condition is unstable so that the level rapidly drops to the point2I with reduction of the current to magnitude I Further evaporationreduces the current faster than the volume until, at a liquid level L,,the current I, generates just enough heat to balance the outflow ofsteam against the entry of fresh water. During this period ofinstability, the pressure differential across capillary tube 12 may bereversed to that excess water is returned to tank 10. The location ofthe operating level L,., depending upon such parameters as thehydrostatic head in vessel 10 and the flow resistance of tube 12, variesfor a given system with the effective outlet opening as determined bythe selected nozzle 20. Generally, this level will lie between marks Land L so that the operating current Ix will range between magnitudes I,and I In FIG. 3 I have shown a modified electrode 21' with an enlargedbottom portion 21a of constant width which operates essentially in thesame manner as the electrode 21 of FIG. 2,

except that the current rise between levels L and L is constant.

FIG. 4 shows another electrode 21 whose enlarged bottom portion 21a" isrounded so that the sharp bends in the line I of FIG. 2 are replaced bymore gradual transitions.

Naturally, the specific shapes illustrated in FIGS. 2-4 are merelyrepresentative of a wide variety of roughly equivalent configurations.

While the electrodes described above were disposed in parallel verticalplanes, they could also be made from a pair of nested strips bent into aJ or similar configuration as illustrated at 121, 122 in the perspectiveview of FIG. 5. It will be apparent that, in this case, the level I.coincides with the lower boundary of inner electrode 122, the operationbeing otherwise the same as previously explained.

The use of strips bent in their dimension of thickness as shown in FIG.5, rather than enlarged in their dimension of width as seen in FIGS.2-4, has the advantage of simpler and therefore less expensivemanufacture of these electrodes which can be made from standard stock ofstainless steel or other suitable metal.

The storage tank 10 of FIG. 1 could also be supplemented or replaced bya supply line of more or less constant water pressure, greater than thehydrostatic head in the completely filled heating chamber 14, aslikewise shown in my prior US. patent identified above.

If the electrode extensions above level L; were insulated rather thanexposed, the heating current would remain at the value I; for any waterlevel between marks L, and L,.

A further configuration of electrodes is shown in FIGS. 6 and 7.Electrodes 31 and 32 are suspended from top 16 and are connected tooperating voltage 24 in any suitable manner (not shown). The electrodeshave an arcuate cross section as shown in FIG. 7 and have a shape at thelower ends thereof which are invertedly nested, one within the other, asshown in FIG. 6. By this laterally inverted nesting, a substantialincrease in the facing area of the electrodes is obtained, whilemaintaining the upper portions of the electrode at a substantial spacingin order to minimize the increase in electrical conductance when chamber14 is filled with water above the level of the short leg of the.I-shaped electrodes. By minimizing the increase in electricalconductance, excessive boiling which could result in spitting of hotwater is limited. Also, the increased spacing reduces electricalconsumption as compared with parallel spacing of electrodes such as inthe embodiment shown in FIG. 5. The embodiment of FIGS. 6 and 7 preventsexcessive surge of steam output when the chamber is filled with waterand maintains a more equalized steam output at the various water levels.

Depending from top 16 are a pair of nonconductive supports 33 having asurface which mates with the curvature of electrodes 31, 32 so that theelectrodes may be mounted thereon, as by suitable rivets 34. The closecontact of the electrodes with the supports provides means formaintaining the electrodes in parallel relationship. The curvature ofthe electrodes improves the rigidity thereof, which is furthermaintained by the conformation with the supports.

It will be noted that the coplanar .l's defined by the electrodes 31, 32of FIGS. 6 and 7 have rounded bight portions, in contrast to the angularones of the electrodes of FIGS. 2(A) and 5, and that their dependinglonger legs alternate with their upstanding shorter legs; thus, thespacing between the two electrodes is considerably smaller in the zoneof overlap than in the region above the level of termination (L FIG. 2)of the two short legs.

What is claimed is:

1. A steam generator comprising an upright heating chamber with an inletin the region of its lower end and an outlet in the region of its upperend, feed means at said inlet for supplying water to said chamber,discharge means connected to said outlet for emitting steam therefrom,support means in said chamber and a pair of juxtaposed electrodes insaid chamber connectable to a source of heating current for vaporizingthe water therein; said electrodes being constituted by elongateelements of generally .l-shaped configuration having each asubstantially vertical long leg depending from said support means nearsaid upper end, a bight portion in the vicinity of said lower end and anupstanding short leg rising from said bight portion, said elements beingspacedly nested with their Js in coplanar relationship and with theirshort legs terminating at substantially the same level above their bightportions.

2. A steam generator as defined in claim 1 wherein said J s arerelatively laterally inverted with alternation of their long

1. A steam generator comprising an upright heating chamber with an inlet in the region of its lower end and an outlet in the region of its upper end, feed means at said inlet for supplying water to said chamber, discharge means connected to said outlet for emitting steam therefrom, support means in said chamber and a pair of juxtaposed electrodes in said chamber connectable to a source of heating current for vaporizing the water therein; said electrodes being constituted by elongate elements of generally Jshaped configuration having each a substantially vertical long leg depending from said support means near said upper end, a bight portion in the vicinity of said lower end and an upstanding short leg rising from said bight portion, said elements being spacedly nested with their J''s in coplanar relationship and with their short legs terminating at substantially the same level above their bight portions.
 2. A steam generator as defined in claim 1 wherein said J''s are relatively laterally inverted with alternation of their long and short legs.
 3. A steam generator as defined in claim 1 wherein said elements are metal strips with a dimension of width transverse to the plane of the J''s.
 4. A steam generator as defined in claim 3 wherein said strips are transversely curved at the upper extremities of said long legs.
 5. A steam generator as defined in claim 4 wherein said support means comprises two members with matingly curved surfaces in contact with said upper extremities. 